This invention relates to the removal of contaminants from gaseous streams, and, more particularly to the removal of sulfur containing compounds from such streams.
Sulfurous contaminants in gaseous streams are often directly present as sulfur dioxide, or are convertible to sulfur dioxide.
For example, the combustion of fuels with a relatively high sulfur content produces an exhaust emission with an objectionable sulfur dioxide content. In addition, many chemical processes produce waste gases with such sulfurous contaminants as carbon disulfide and hydrogen sulfide.
The conversion of carbon disulfide, hydrogen sulfide, and the like to sulfur dioxide is easily accomplished. The sulfur dioxide can then be catalytically converted to sulfur trioxide, which is, in turn, converted to sulfuric acid.
In the process disclosed in U.S. Pat. No. 3,119,663, which issued Jan. 28, 1964 to H. Furkert, carbon disulfide and hydrogen sulfide are converted to sulfur trioxide using vanadium catalyst of the kind conventionally used for the oxidation of sulfur dioxide to sulfur trioxide. This technique is accompanied by processing and equipment complexities, but suitable vanadium catalysts are widely known. In the typical case they consist of compounds of vanadium and potassium on an inert carrier, as illustratively disclosed in U.S. Pat. No. 3,226,338, which issued to H. L. Riley et al on Dec. 28, 1965. Other illustrative catalysts are disclosed in U.S. Pat. No. 2,799,560, which issued to P. Davies on July 16, 1957; U.S. Pat. No. 2,418,851, which issued to E. F. Rosenblatt on Apr. 15, 1947; U.S. Pat. No. 1,862,825, which issued to N. A. Laury on June 14, 1932; U.S. Pat. No. 1,696,546, which issued to A. O. Jaeger et al. on Dec. 25, 1928; etcc.
Supported catalysts of the foregoing type are in wide use and have been used, for example, in the removal of sulfur dioxide from flue gas as shown in U.S. Pat. No. 3,615,196, which issued to A. B. Welty, Jr., et al. on Oct. 26, 1971. Among the objections to the Welty technique are that it requires a mechanically complex, rotating reactor in which the catalyst is supported, and it makes use of an air stream that is heated above the temperature of the stack gases.
Non-supported catalysts have also been used in converting sulfur dioxide to sulfur trioxide, as disclosed in U.S. Pat. No. 2,381,908 which issued to D. M. Hurt et al. on Aug. 14, 1945 and British Pat. Nos. 1,136,903 and 1,244,978 which issued to C. N. Kenney et al on Dec. 18, 1968 and Sept. 2, 1971. These techniques are suitable for the production of sulfur trioxide and sulfuric acid, but they are not suitable for the removal of contaminants from gaseous streams, since only a portion of the sulfur dioxide in the exhaust stream is converted.
Accordingly, it is an object of the invention to facilitate the removal of sulfurous contaminants from gaseous streams. A related object is to simplify the procedure and equipment used for so doing.
Another object is to eliminate the need for a supported catalyst in the removal of sulfurous contaminants from gaseous streams. A related object is to achieve the substantial removal of such contaminants, even when present in low considerations, without the need for a supported catalyst.
A further object is to achieve the removal of a substantial portion of the sulfur dioxide resulting from the combustion of fuels containing a relatively high percentage of sulfur. A related object is to achieve the removal of 90 percent of the sulfur dioxide resulting from the combustion of fuel with more than 1 percent sulfur.